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The Netwalker is a very small laptop computer with an ARM CPU, running
Ubuntu GNU/Linux. As it uses flash memory instead of a hard drive, you
need a special procedure to update the kernel (the Netwalker does not
use standard boot loader like Lilo or Grub). This small how to
describes how to compile the Linux kernel for the Netwalker, and then
how to flash the kernel. I will provide interesting kernel hacks later
on this blog.

Then, you can grab the Sharp's Netwalker kernel configuration in
/sys/config.gz . Uncompress it, rename it ".config", and move it in
the kernel source directory. Add in the kernel config the option
CONFIG_KS7010_SDIO for the Wifi (strangely it is not present in
/sys/config.gz).

Finally, compile the Linux kernel as usual, and install it.

Flashing the kernel

You need a 2 Gb (or more) microSD / microSDHC card. BEWARE : the
card will be reformatted and any data on the card will be deleted! You
should also make a safe copy of any data on the Netwalker.

Create a microSD recovery card; instruction are in Japanese on
Sharp's website, so here is a
summary.

Insert the microSD card in the Netwalker, connect the Netwalker to
Internet, and run the script. The script will set up the recovery
card. It downloads many data (about 1 Gb) and thus it takes several
hours.

The microSD recovery card can be used to reset the Netwalker,
reflashing the kernel and erasing all data. This can be done by
shutting down the Netwalker, and pressing both mouse button at start-
up (you need to press the button quite a long time). However, this is
not what we want to do: the objective of this how-to is to flash only
the kernel. To do so, follow the next steps.

Mount the microSD card. This can be done with these commands:

mkdir /tmp/test
mount /dev/mmcblk0p1 /tmp/test

Edit file /tmp/test/firmware/spider.srp ,and remove the line
"5,ubi.img". This line is responsible for erasing all data on the
Netwalker. The next line (4,zImage) is responsible for flashing the
kernel, so we keep it.

Replace /tmp/test/firmware/zImage by the new kernel image
(typically /boot/vmlinuzXXX).

Edit file /tmp/test/usr/local/bin/update_spider.sh . At line 47 and
following, add /tmp/test before /usr/local/bin/... (there is 5 lines
to modify).

Connect the Netwalker's power cable.

Run /tmp/test/usr/local/bin/update_spider.sh . Then press "y", wait
a few second and press any key to exit.

The kernel has been flashed! Now, reboot the Netwalker and enjoy
your new kernel!